Radiation therapy, which may be used instead of or after surgery, damages the DNA in cancer cells, preventing the cells from replicating and causing the tumor to shrink. There are two ways to deliver radiation: by aiming an external beam of radiation at the tumor, or by surgically implanting small radioactive pellets into the prostate gland, an approach called brachytherapy.
Several types of external beam radiation exist. These include three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), proton beam therapy, CyberKnife, and TomoTherapy. Depending on how the treatment is delivered, treatment sessions can last from about 15 minutes to an hour or longer. Because the dose of radiation must be spread out over time, treatments are generally repeated five times a week for about eight weeks.
With brachytherapy, a doctor inserts the radioactive seeds into the prostate, and the seeds are left in place permanently. Over time, the seeds give off less and less radiation until they become inert.